Add test for listing carriers and assert that at least one carrier has a code equal to "gls".

- Add test for listing carriers
- Assert that at least one carrier has a code equal to "gls"

test.py

@@ -34,5 +34,9 @@ class TestKeyDelivery(TestCase):
         response = self.keydelivery.realtime("gls", "483432314669")
         self.assertEqual(response["code"], 200)
 
+    def test_list_carriers(self):
+        response = self.keydelivery.list_carriers()
+        self.assertTrue(any([carrier["code"] == "gls" for carrier in response["data"]]))
+        
 if __name__ == "__main__":
     main()